Mobile IP (MIP) is described in a number of documents developed in the IETF (Internet Engineering Task Force) (www.ietf.org). MIP provides for mobility management for a Mobile Node (MN) Home address (HoA) by redirecting (e.g., tunneling) packets that are received at a Home Agent (HA), and that are directed from a Correspondent Node (CN) source address to a MN HoA, towards a MN Care of Address (CoA), at which the MN HoA is routable. Typically, the MN CoA is the address of the Foreign Agent (FA) within the Access Router to which the MN is directly attached, i.e., connected to without an intermediate node being present between the Access Router and MN Similarly, packets received at the FA from the MN, that are directed from the MN HoA to the CN, are redirected to the HA using a redirecting packet, where the redirected packet is retrieved from the redirecting packet and forwarded by standard Internet routing towards the CN destination address. MIP signaling between the MN and the HA, maintains the MN CoA/MN HoA binding at the HA and the FA, and updates it to each new CoA value as the MN moves between Access Routers (FAs), and hence across the routing topology. The HA issues routing adverts for HoA prefixes at that HA, and MNs are allocated HoAs from said advertised prefixes to ensure that packets address towards the MN HoA are forwarded via the HA.
The known MIP FA is typically separated from the MN by a single link which may be a fixed or wireless link, with each MN on a single FA having a unique link-layer address. The identity of a MN, that sends an upstream packet to the FA, is typically known by the link-layer source address of link-layer frames that carry the packet over the access link. The FA then forwards packets by comparing the source address of the packet to the HoAs stored in mobility bindings within the FA for that identified MN. The FA then determines, from the matching mobility binding, the address of the associated MIP HA to which the received packet should be redirected. When downstream redirecting packets are received from the HA and the redirected packet is recovered, then the MN receiver is identified at the FA using the combination of the HA source address of the redirecting packet (the HA address) and the destination address of the redirected packet (the MN HoA). These addresses identify a unique mobility binding at the FA, from which the link-layer identity of the MN can be determined so that the packet can be forwarded in link-layer frames to that MN.
When the MN has multiple HoAs from one or more HAs then the link-layer and packet information received at the FA may not uniquely identify the HA that is associated with the HoA source address of the upstream packet, due to the MN having multiple HoAs from overlapping address spaces. Additional information needs to be received at the FA with each packet to enable the FA to discriminate between the multiple binding entries that contain the same HoA value. Additionally, downstream packet information that is received at the FA may not be able to uniquely identify the MN receiver if the combination of the HA address and the HoA address is not unique at the FA because, for example, multiple different HAs employ the same HA address and the same HoA address prefix.
In addition, when a regional MIP node exists between the FA and the HA, and upstream packets are directed through, and switched by, that regional MIP node, then the FA needs to provide information in the redirecting packet to enable the regional MIP node to be able to forward the packet to the correct upstream HA that is associated with the HoA in the source address of the packet. The HoA value itself is not sufficient because once again the HoA from different HAs can reuse the same value leading to forwarding ambiguity at the regional MIP node. Similarly, downstream packets received at the FA are now forwarded using the combination of the regional MIP node address in the redirecting packet and the HoA in the redirected packet, but this combination is again not necessarily unique even if the HoA/HA address combination is unique, because the HA address has been lost from the redirecting packet through the regional MIP node.
Similarly in some cases, a specific problem further occurs with multicast packets that are forwarded from the HA to the FA and onto the MN because the destination address of the packet for the access link is a multicast address. This multicast address has to be hidden in standard MIP forwarding by using an encapsulating tunnel that includes the HoA as the destination address so that the target MN can be identified and reached. This additional encapsulation is inefficient over the access link and should ideally be avoided, but its removal creates forwarding ambiguity at the FA and demultiplexing ambiguity at the MN (e.g. with which (MN,HA,HoA is this multicast content associated).
One prior art technique uses a composite packet that is received at the FA for the specific case that the MN and FA are separated by an inter-working function (IWF) to resolve forwarding ambiguities due to the loss of the MN specific link-layer identifier between the IWF and the FA, that exists between the MN and the IWF. The composite packet contains both the upstream packet and the Network Access Identifier (NAI) of the MN sender, the NAI identifying the username@domain of the MN (or some other unique MN identifier) so that the FA can determine the MN and its set of mobility bindings for forwarding purposes. Similarly, downstream packets are matched to a unique mobility binding to identify the MN, and then the composite packet is formed so that the IwF can map the NAI in the composite packet into the MN specific link-layer identifier that exists between the IWF and the MN for forwarding purposes.
This technique does not however provide support for resolving the ambiguities in the downstream forwarding/demultiplexing for redirecting packets received at the FA and the MN, nor for upstream packets when the MN has multiple HoAs from different HAs for the same NAI (or equivalent composite packet information). In addition, the NAI is also a very large identifier and basing forwarding in the FA on IP layer information such as the HoA and the NAI is less efficient than using link-layer identifiers, as exemplified by Multi-Protocol Label Switching (MPLS) systems.
In view of the above discussion, it should be apparent that there is a need for improved methods of forwarding packets in mobility networks to remove the forwarding ambiguities associated with multiple HoAs from multiple HAs for each MN.